If you've been clamoring for multiple account support in the Instagram app, you might soon be in luck. Some iPhone users, including our own Mat Smith, are seeing the feature pop up on iOS. If you'll recall, the ability to sign in to multiple accounts and toggle back and forth when posting made an appearance back in November on the Instagram Android app.
You had to manually download an APK to take advantage then, but that's not necessary in iOS. Since multiple account support is only available to a few, it appears to still be in the testing phase. Hopefully that'll change soon as Instagram is one of the few social apps that doesn't allow you to easily switch between accounts.